A previously proposed fluid pump has an inner rotor, an outer rotor and a pump housing. The inner rotor includes external teeth, and the outer rotor includes internal teeth for meshing with the external teeth. The pump housing receives the inner rotor and the outer rotor. When the inner rotor is rotated, a rotational force of the inner rotor is transmitted from the external teeth to the internal teeth. Thereby, the outer rotor is also rotated. When the inner rotor and the outer rotor are rotated, the volume of the respective pump chambers, which are formed between the external teeth and the internal teeth, changes. In response to increasing of the volume of the pump chamber, the fluid is drawn into the pump chamber through a suction passage formed in the pump housing. Thereafter, in response to decreasing of the volume of the pump chamber, the fluid is compressed in the pump chamber and is discharged from the pump chamber.
A suction groove, which is communicated with the suction passage, is formed in an inside wall surface of the pump housing. The suction groove is shaped to extend along a rotational path of the external teeth and a rotational path of the internal teeth, and the suction groove increases a radial extent of a fluid passage, through which the fluid is supplied from the suction passage into the pump chamber (see, for example, JP2013-60901A).
Various developments have been made to improve the pump efficiency of the fluid pump through elaborations on, for example, configurations of the suction groove and the suction passage. Lately, demand for energy saving has been progressively increased, and thereby a further improvement of the pump efficiency has been demanded.